If you want to purchase an exhibit board that has been manufactured to specifically match the NHD rule specifications, here is a link to that company:
They are $14 + shipping. You might want to go in together with other groups to make the shipping cheaper, if you're planning to order through them.
YOU DO NOT HAVE TO USE THESE BOARDS, but you need to make a decision SOON about what kind of board you are going to use! You can get cardboard from other sources or use a different product (foam board, wood, or anything else you can imagine that fits the parameters). Mr. Nesbitt is willing to get large sheets of cardboard from Costco - if that is an option you want to use - please tell Mrs. Doughty that you are choosing this option.